Journal of Health and Safety at Work

Acoustic analysis of a semi-anechoic chamber with intersection

P. Nassiri

Introduction: The previous studies have used fibrous absorbents usually in the form of cone-shaped wedges for making anechoic and semi-anechoic chambers which their design and construction have been costly and difficult. The present study aimed to design a semi-anechoic chamber, using rectangular fibrous absorbents and also perform acoustic analysis for it.

Material and Method: In the present study, which was done at semi-anechoic chamber of the laboratory in Tehran University of Medical Sciences. The reverberation time, the total surface and the absorption surface of the chamber were determined, before and after the design and also they were compared with the target values. Intersection layout of the rectangular fibrous absorbents were design using graphic design software (AutoCAD and 3Ds Max). before design, the reverberation time were measured according to ISO 3382:2000. The reverberation time in redesigned chamber was also calculated through retention time equation (Sabine). Moreover, Sabin’s formula was applied for determining the absorption surface and the total surface of the chamber, before and after the design.

Result: Before design, the reverberation time in the cut-off frequency of 250 Hz according to ISO 3382:2000 was determined 0.3 second. Moreover, the total chamber surface was 47.97 m2. CAD software estimated at least 253 rectangular absorbents with dimensions of 50×18 cm. After design, the absorption surface and the total chamber surface were obtained 46.32 m2 and92.64 m2, respectively and the reverberation time in the mentioned frequency was 0.07 (s).

Conclusion: According to the results, it can be concluded that the suggested intersection layout of rectangular fibrous absorbents can be used as a reliable method in order to reduce the reverberation time and to gain lower cut-off frequency for construct a semi anechoic chamber with the high efficiency.

An investigation of Extremely Low Frequency (ELF) Electromagnetic field emitted by common Laptops

R. Golmohammadi

Introduction: Electromagnetic field emitted by laptops are known as extremely low frequency (ELF) Waves. The aim of this study was to investigate the intensity of electric and magnetic field with extremely low frequency emitted by common laptops.

Material and Method: Intensity of electric and magnetic field were measured on four sides of 40 common by used laptop at the distance of 30, 60 and 90 cm. Measurements ere done according to standard in four functional model including: non-performing turned on, sleep mode, performing office program and performing audio visual files.

Result: Magnetic field values for all laptops were almost constant and about 28-32 mA/m. The results of measurements related to the electric field showed different values at distances of 30, 60 and 90 cm around the laptops on four sides. Moreover, mean electric field on the keyboard at the four operating modes were statistically different for DELL and hp laptops (P< 0/05).

Conclusion: The results of this study showed that laptops produce extremely low frequency (ELF) electric and magnetic fields which their intensity depends on laptop type, laptop operation mode and the location of the measurement.

Using silver nano particles for sampling of toxic mercury vapors from industrial air sample

H. Shirkhanloo

Introduction: Mercury is one of the toxic metals that damages the nervous system and kidneys. Therefore, monitoring of mercury vapors in the environments is essential.

Material and Method: A new adsorbent was made from silver nanoparticles on a bed of quartz. The nano-adsorbent was capable for sampling of the trace amounts of mercury vapor from air. In this study, the required mercury vapor was generate by hydride generation atomic absorption spectrometry and the necessary analysis was performed by cold vapor atomic absorption spectrometry.

Results: Mercury vapors in the Stationary phase, were concentrated as much as 2300 times (Atomic absorption detection limit was 1.15 microgram per liter of air). Thus by this stationary phase, the trace amounts of mercury vapors can be detected up to 0.5 nano gram per liter of air. The detected value of the presented method is 200 times lower than the occupational safety and health administration (OSHA) standards for mercury vapors. Heater accessory at the temperature of 245 °C was used for thermal desorption of mercury from nano silver adsorbent. Optimal time of desorption was obtained 150 seconds and the Repeatability of the method was 58 times. The mercury vapors absorbed on nano silver adsorbent could be maintained at 80 days at the room temperature (25 °C).

Conclusion: The presented adsorbent is very useful for sampling of the trace amounts of mercury vapors from air. Moreover, it can be regenerated easily is suitable or sampling at 25 to 70 °C. Due to oxidation of silver and reduction in uptake of nanoparticles, oven temperature of 245 °C is used for the recovery of metallic silver. Low amount of adsorbent, high absorbency, high repeatability for sampling, low cost and high accuracy are of the advantages of the presented method.

The effect of ergonomic training and intervention on reducing occupational stress among computer users

T. Yektaee

Introduction: Nowadays, computers are integral component of all workplaces. Moreover, employees healthstatus is directly associated with their occupational stress level. The aim of the present study was to investigative the effect of ergonomic training and intervention on reduction of occupational stress among computer users in welfare organization in Rasht city.

Material and Method: In this semi experimental study, 283 female computer users, who were 30-40 years old with work experience of 5-15 years, were chosen as sample. The participants had at least one year experience of using computer and they had worked 3-4 hours with computer daily. The Osipow occupational stress questionnaire (1987) with Cronbach alpha 87% was applied for estimation of occupational stress. Then, 46 participants with moderate to high level of stress were selected and randomly divided into case ad control groups. Participants in a case group received practical and theoretical ergonomic training and also interventions (including armrest, foot rest, cushion, posture correction, reduction o work time duration, adjustment of the seat height according to individuals height, adjustment of eye-monitor distance). Finally, the obtained data were compared to those of control group, using covariance.

Result: According to covariance analysis, ergonomic training and interventions lead to reduction of occupational stress of computer users.

Conclusion: Training computer users and informing them of the ergonomic principals and also providing interventions such as correction of posture, reducing duration of work time, using armrest and footrest would have significant implication in reducing occupational stress among computer users.

A study of students cognitive performance under noise exposure, using Continuous Performance Test “Study on the effects of noise on cognitive performances”

M. J. Jafari

Introduction: In the most industrial environment, workers are exposed to noise everyday. Exposure to this physical hazardous agent can cause immediate as well as delayed adverse effects. Cognitive performance decrement is one of the adverse effects of noise exposure which its main consequences is occupational accidents. This study attempted examine the effect of exposure to different levels of noise with harmonic indices of neutral, treble and bass on the cognitive performance.

Material and Method: In this analytical-descriptive study, the cognitive tests were performed by 33 students, aged 23-35 years. During the tests, participants were exposed to three type of noise including neutral, treble and bass at 4 different levels of 45, 75, 85 and 95 decibels. In order to assess students cognitive performance, continuous performance test (CTP) software was employed, which investigated attrition and reaction time.

Result: The results of this study revealed that exposure to neutral noises with Noise Harmonic Index (NHI) of +3dB at the frequency of 1000 Hz, the maximum percentage of attention (99.88 %) was belonged to Sound Pressure Level (SPL) of 95 decibels. Maximum percentage of attention due to exposure to the treble noise with NIH -105 dB at the noise frequency of 8000 Hz (100%) and bass noise with NIH of 407 dB at the frequency of 500 Hz (99.92%) were belonged to the SPL of 95 and 85 dBA, respectively. Moreover, the result showed that the effect of bass noise with NIH of 4.5 dB and frequency of 500 Hz on reduction of attention were more than treble noise with NIH of -105 dB and frequency of 8000 Hz. Under exposure to neutral noise with NIH of 3 dB and frequency of 1000 Hz, the longest reaction time (2.594 Second) was observed at the SPL of 85 dBA. The longest reaction time for treble noise with NIH of -105 dB and frequency of 8000 Hz (2.786 Second) and for the bass noises with NIH of 4.5 dB and frequency of 500 Hz (2.594 Second) were also belonged to the SPL of 85 and 75 dBA, respectively.

Conclusion: The results showed that bass noises (frequency of 500 Hz) increased reaction time, in comparison with treble noises (frequency of 8000 Hz).

Introducing a method for Health, Safety and Environmental (HSE) risk assessment, using multi-criteria decision making (MCDM) techniques: a case study in power plant construction

I. Mohammadfam

Introduction: Nowadays, using multi attribute decision making (MADM) techniques in HSE hazard rating have been widely increased. On the other hand, Analytical Network process (ANP) methods has a high flexibility and accuracy in decision ranking. Therefore, the combination of the two mentioned approaches can provide a more precise prioritization for HSE hazards. Using ANP techniques, in this research a method for accurate rating of HSE hazards in the construction procedure of combined cycle power plant was presented.

Material and Method: In this study, first, the overall structure and components of ANP method were identified and the connections between its components were determined. Then, the determined structure and components were modeled, using super decision software. In the next stage, pair companions were performed between an criteria and sub-criteria with respect to HSE experts opinions, Finally, selected HSE hazards were prioritized and compared according to the presented ANP method and the common available method.

Result: According to the results, common risk assessment method is not able to prioritized risk accurately. While the current method classified the ten main identified hazards in 4 general categories, the presented method in this study could prioritized then in 7 categories.

Conclusion: The suggested ANP model could provide a more accurate prioritization for hazards in comparison with current methods because of considering five qualitative indices. This allows an optimal allocation of organizational resources for controlling hazards.

Safety culture assessment among laboratory personnel of a petrochemical company

G. A. Shirali

Introduction: Investigation of accidents have shown that more than 90% of industrial accidents are related to human aspects. What is more, safe behaviors can not be institutionalized in industries by only using technical-engineering measures and enacting safety rules. Building a positive and effective safety culture can make individuals aware of hazards and consequently reduce accidents in the workplace.

Material and Method: In this analytical-descriptive study, a standardized safety culture questionnaire was used. The questionnaire comprised of 40 question including five dimensions of: training, work environment, safety priority, information exchanges and management commitment. In this regard, the questionnaire was distributed among personnel of three laboratories in a petrochemical company. Five point Likert scale was for recording the responses.

Result: The mean score for safety culture was 136.7 for laboratory personnel which was considered positive according to the presented definition. In this sense, safety priority and management commitment with score of 31.9 and 25.2 obtained respectively the dimensions of safety culture.

Conclusion: Strong and positive safety culture among laboratory personnel would prevent incidence of many occupational accidents. In another word, it would help organizations to facilitate access to higher standards.

Modeling and verification of acoustic wave propagation in indoors using Sabine model in turbine hall of a gas power plant

H. Ekhlas

Introduction: Noise is one of hazardous agents of workplaces in industries. Electric industries and power plants are among industries in which noise pollution should be taken into account. This study aimed to develop and verify a statistical model for acoustic wave propagation in an indoor environment for noise related risk reduction management.

Material and Method: This theoretical-experimental study was performed in a gas power plant with nominal capacity of 648 MW including four gas turbine with nominal capacity of 162 MW. The relations between sound power level and sound pressure level in indoor environments were used for developing the statistical model. Moreover, verification of the obtained data was done by a field inside a turbine hall study using ISO9612 standard method.

Result: Comparison of results from the field and the theoretical study showed no significant differences. The differences between predicted value and field measurements was, in average, less than 0.5 db. This shows the acceptable accuracy of the presented model in estimating the workplace noise level, according to the real functional conditions of the noise sources.

Conclusion: The presented model is easy and practical and allows managers to model scenarios of noise pollution reduction in indoor environments, before huge expenses of actual control measures. This method is faster comparing to numerical modeling methods. Furthermore, its accuracy is also acceptable.